The early detection of colon cancer is frequently very difficult, since the colorectal cancers or colon tumors very seldom cause symptoms. The colorectal cancers almost always arise from initially benign colon polyps that must be removed in good time before they become carcinogenic. Of recent years, virtual colonography has been developed as a non-invasive method for diagnosing colon polyps as an alternative to colonoscopy. The procedure is based on a visualization of a 3D image data record, obtained by way of computed tomography, of the abdominal region of a patient. In advance of the investigation, it is customary to clean the colon and to mark stool remainders with the aid of a contrast medium. During the investigation, carbon dioxide is introduced into the colon through a small catheter in order to enable a better reconstruction of the intestinal walls.
A number of methods are applied nowadays to visualize the data. One of these methods comprises the so-called fly-through visualization mode, in the case of which a virtual camera that serves the purpose of 3D utilization is moved along the closed colon in a manner similar to a colonoscopy. In accordance with an alternative method, the so-called colon-flattening method, the inner walls of the colon are displayed as a plane. The disadvantage of this method is, however, that it requires complicated pre-processing steps and is therefore computationally complicated. In addition, the colon walls are distorted by their display in a plane, and so it becomes difficult to detect small of flat polyps. A combined method is described in US 2008/0055308 A1. A virtual camera is moved along the centerline of a colon, and the inner walls of the colon can be displayed both in a perspective image and in a developed, flat image.